Geomicrobial prospecting method for petroleum



GEONHCROBIAL PROSPECTING METHQD FGR PETRQLEUM John B. Davis, Dallas, Tex., assignor, by mesne assignments, to Socony Mobil Oil Compan Inc, a corporation of New York No Drawing. Application August 28, 1952, Serial No. 306,957

7 Claims. (Cl. 195-1035) This invention relates to prospecting for subterranean petroleum deposits and relates more particularly to a microbial method for locating such deposits.

It has been postulated that hydrocarbons emanate from a subterranean petroleum oil or gas deposit upwardly through the earth overlying the deposit and that the presence of these hydrocarbons or their reaction products in the earth is indicative of the underlying deposit. Accordingly, various methods based on the concept of emanation or migration of hydrocarbons from subterranean deposits have been proposed for locating the deposits. Among such methods are those which involve the detection of hydrocarbon-consuming microbes in the earth, it being taken that such microbes exist and thrive in the earth by virtue of their ability to utilize as nutrient, or as an energy source, the hydrocarbons migrating from the underlying petroleum deposit, and that the presence of such microbes in the earth is thereby indicative of the presence of the underlying petroleum deposit. In

tained in an atmosphere containing oxygen and a gaseous petroleum hydrocarbon. Any hydrocarbon-consuming microbes which may have been contained in each of the earth samples will consume the atmosphere and the rate at which the atmosphere 1s consumed, as measured by the decrease in pressure of the atmosphere, is regarded as a measure of the number of hydrocarbon-consuming microbes originally in each sample. The number of microbes thus determined is then related to the location of the sampling points to detect anomalous variations petroleum deposit.

However, consumption of the atmosphere is not a speand oxidizable organic matter present in the earth samples are capable of consuming the oxygen. Thus, anomalous variations in the number of microbes per unit thee large numbers of hydrocarbon-consuming microbes. Another method of distinguishing involves analysis of the atmosphere to detect a decrease in the quantity of the hydrocarbon in the atmosphere but this method requires involved and expensive analytical techniques.

It is an object of this invention to provide a geomicrobial prospecting method for subterranean petroleum deposits. It is another object of this invention to provide a method for detecting the presence of hydrocarbonconsuming microbes in earth samples.

as being due to causes other than the action of hydrocarbon-consuming microbes in the earth sample. These and other objects of the invention Will become apparent from the following description thereof.

In accordance with my invention, earth samples taken from a prospect zone are contacted with oxygen and ban-consuming microbes and the intensity of the radioactivity is a measure of the number of hydrocarbonconsuming microbes in the earth sample.

In the practice of the invention, earth samples are collected at spaced intervals over a zone to be prospected for an underlying petroleum deposit. The samples are taken from points below the surface in order to avoid samples which have been affected by weathering, contamination, or other factors rendering them not representative of the prospect area. Generally, samples taken at depths greater than about one foot will be satisfactory although local conditions may require that the sampling be made at greater depths. However, since hydrocarbonconsuming microbes are aerobic, the samples must be taken at points where the earth contains sufiicient oxygen to enable these microbes to survive and therefore the samples must be taken at depths above the water table.

'in and the admixture of water with each of the earth samples may not be required. Where water is admixed with each earth sample, any suitable amount of water, such as about 35 percent by weight of the earth sample, may be employed.

Where water is admixed with each earth sample, it is preferred, in order to obtain increased metabolic activity of any hydrocarbon-consuming microbes, to provide in the reaction mixture inorganic salts utilized in microbial growth and these salts may be dissolved in the water admixed with the earth sample. Such salts include those furnishing ammonium, ferrous or ferric, magnesium, phosphate, and sulfate ions. The concentrations of the salts may vary widely although the concentra ions must be below those which will have an inhibiting or poisoning effect on the microbes. Thus the concentrations of iron should not be greater than about parts per million while the concentration of calcium may be as high as 1000 parts per million. In addition, it is preferred that the pH of the medium be between about 7.2 and 7.6 and adjustment of the pH of the aqueous medium may be made by addition of acid or base as required.

A suitable aqueous medium for admixture with each earth sample has the following composition:

Ingredient:

The medium is prepared by dissolving the salts in the water and sterilizing by heating; for example, in an autoclave with steam at 20 pound per square inch gage for 20 minutes. After sterilizing, the pH of the medium is adjusted to a value between 7.2 and 7.6 by addition of a sterile solution of sodium hydroxide whose concen tration may be about one normal.

It is preferred that the hydrocarbon whose molecules contain carbon having an atomic weight of 14 contacted with each of the earth samples be a gaseous hydrocarbon. Methane, ethane, or propane i suitable. However, it is preferred not to employ methane since methane may be present in the earth as a result of vegetative decomposition or for other reasons not related to the presence of an underlying petroleum deposit and the presence of methane-consuming microbes in the earth samples is therefore not a positive indication of an underlying petroleum deposit unless all other factors accounting for the presence of methane in the earth samples can be definitely eliminated. While gaseous hydrocarbons are to be preferred, it is possible to employ liquid hydrocarbons such as dodecane, tetradecane, or hexadecane or solid hydrocarbons such as tetracosane, hexacosane, or octacosane, or mixtures of gaseous, liquid, or solid hydrocarbons.

The hydrocarbons whose molecules contain carbon having an atomic weight of 14 may be prepared by conventional methods for the preparation of radioactive hydrocarbons and no further description will be given of their methods of preparation since these methods are outside the scope of this invention.

Where the hydrocarbon to be employed is a gaseous hydrocarbon, each of the earth samples, after being admixed with the water and inorganic salts if either or both are employed, is separately exposed to an atmosphere of the gaseous hydrocarbon and oxygen. The oxygen may be pure oxygen or air may be employed to provide the oxygen. Exposure of the earth samples to the atmosphere of gaseous hydrocarbon and oxygen is conveniently effected employing a flask, bottle, or other type of chamber provided with a gas inlet or inlets that can be closed to provide a sealed reaction zone for the reaction mixture. Where the hydrocarbon to be employed is a liquid or solid hydrocarbon, a similar type of sealed reaction zone may be employed for the reaction mixture. However, where the hydrocarbon to be employed is a liquid or solid hydrocarbon, an open reaction vessel or chamber may be employed, the oxygen being supplied from the air, provided that the portion of the reaction mixture analyzed for carbon atoms having an atomic weight of 14 which have entered into a microbial metabolic process is not a gaseous portion or, if a gaseous portion, is trapped or otherwise collected from the reaction zone so that it may be analyzed.

It is not essential that the oxygen, or oxygen and hydrocarbon where a gaseous hydrocarbon is employed, contacted with the earth sample be static. If desired, the oxygen, or oxygen and gaseous hydrocarbon, may be replaced continually or intermittently during the period of time that the earth sample is contacted therewith. For

xarnple, with the earth sample contained in a flask or other suitable apparatus having a gas inlet and a gas outlet, the oxygen, or oxygen and gaseous hydrocarbon, may be passed into the apparatus through the gas inlet to contact the earth sample and then out through the gas outlet. Where contacting of the earth sample with the oxygen, or oxygen and gaseous hydrocarbon, is carried out by a procedure of this sort, the oxygen, or oxygen and gaseous hydrocarbon, removed from contact with the earth sample is part of the reaction mixture and will contain microbial metabolism product of the hydrocarbon.

The earth sample, the hydrocarbon, and the oxygen, in addition to the water and the inorganic smt where employed, comprising the reaction mixture, are maintained in contact with each other at an incubating temperature for a sufficient time for the formation of microbial metabolism products from the hydrocarbon. Incubating temperatures may be those commonly employed for growth or multiplication of microbial cultures and convenient temperatures are those between about 50 F. and F. Microbial metabolism products are formed from the hydrocarbon in detectable quantities within a period of time as short as one-half hour depending upon the incubation temperature. However, the components of the reaction mixture may be maintained in contact with each other for longer periods of time such as several days or several weeks to obtain larger quantities of the microbial metabolism products from the hydrocarbon and thereby increase the ease and accuracy of the analysis for carbon atoms having an atomic weight of 14 which have entered into the microbial metabolic process. It may occasionally be found that no detectable quantities of microbial metabolism products are formed from the hydrocarbon until the components of the reaction mixture have been in contact with each other for a time greater than about 25 days but thereafter detectable quantities are formed. This phenomenon is recognized as being due to the absence initially in the earth sample of hydrocarbon-consuming microbes but the presence initially in the earth sample of microbe which are capable of adapting themselves with time to consume hydrocarbons and which have adapted themselves to consume the hydrocanbon in the reaction mix-ture. The time required for these microbes to adapt themselves to consume hydrocarbons is known in the art as the adaptation time and, where formation of microbial metabolism products from the hydrocarbon does not occur until after the adaptation time, the formation of these products is disregarded with respect to being indicative of the presence of an underlying petroleum reservoir. The adaptation time may vary depending upon the temperature and the type of microbes and is determinable by those skilled in the art.

Where information as to the number of hydrocarbon-consuming microbes per unit amount of earth sample is desired, a known amount of each earth sample from the prospect zone isemployed in the reaction mixture. Further, in these cases, since the number of hydro carbon-consuming microbes per unit amount of earth sample and the temperature of incubation govern the quantity of microbial metabolism products produced per unit time from the hydrocarbon, it is preferred to employ awn-roe ferent lengths of time the components of the reaction mixture are in contact with each other. However, it is possible to make corrections for difierences in the temperatures of incubation for each reaction mixture and for differences in the time the components of each reaccontact with each other, of incubation for each tion mixture are maintained in and therefore the temperatures reaction mixture need not be the components of each reaction mixture are maintained in contact with each other need not be the same.

As stated hereinabove, the common microbial metabolism products are microbial protoplasm and carbon dioxide. Analysis of at least a portion of the reaction mixture for carbon atoms having an atomic weight of 14 which have entered into a microbial metabolic process may be made by analysis of a portion of all of the reaction mixture for carbon dioxide the molecules of which contain carbon having an atomic weight of 14, for microbial protoplasm the molecules of which contain carbon dioxide having an atomic weight of 14, or for a material derived from the carbon dioxide or the microbial protoplasm the molecules having an atomic weight of 14. The carbon dioxide and the microbial protoplasm formed by microbial metabolism from the hydrocarbon Whose molecules contain carbon having an atomic weight of 14 and any material derived from the carbon dioxide or the microbial protoplasm will be radioactive and analysis therefor can be made simply by separating the hydrocarbon from the reaction mixture or portion thereof selected for analysis and determining the extent of the radioactivity of the carbon dioxide, the microbial protoplasm,

mixture selected for analysis will be proportional to the number of hydrocarbon-consuming microbes in the earth sample.

Separation of the hydrocarbon from the reaction mixture can be efiected in a number of Ways. For example, where analysis is to be made for carbon dioxide the molecules of which contain carbon having an atomic weight of 14, the hydrocarbon may be separated from the carbon dioxide by exposing the mixture thereof to a solution of a base such as sodium or potassium hydroxide whereby the carbon dioxide is collected in the solution as the carbonate of the cation of the base. This may be accomplished by maintaining a separate reservoir of a solution of the base in the reaction zone where contacting of the earth sample with the hydrocarbon and oxygen is carried out or by flushing the gas mixture from the reaction zone and contacting it with a solution of the base. Where the oxygen or oxygen and gaseous hydrocarbon is continually or intermittently replaced during contact with the earth sample, the replaced atmosphere may be passed in contact with a solution of the base. The solution of the base containing the carbon dioxide as the carbonate of the cation of the base may then be treated with acid to liberate the carbon dioxide and the intensity of the radioactivity of the carbon dioxide measured. Preferably, however, the solution of the base is treated with barium chloride to precipitate the carbon dioxide as insoluble barium carbonate, the barium carbonate filtered from the solution, and the intensity of the radioactivity of the barium carbonate thus derived from the carbon dioxide measured.

Where analysis of at least a portion of the reaction mixture is to be made for microbial protoplasm the molecules of which contain carbon having an atomic weight of 14 is to be made, various procedures may likewise be employed for separating the microbial protoplasm from the hydrocarbon. Where the hydrocarbon employed is a gaseous hydrocarbon, the soil sample may be flushed with a non-radioactive gas to remove the gaseous hydrocarbon. The gas employed for flushing may be a non- The earth sample, following separa tion from the hydrocarbon, may, without further treatment, be analyzed for microbial protoplasm the molecules of which contain carbon having an atomic Weight of 14 by measuring the intensity may be then separated from the earth sample for analysis of carbon having an atomic weight of 14 by measurement of intensity of radioactivity. Alternatively, the earth sample may be brought quickly to a mobile laboratory or testing unit, apparatus, and contacted the molecules of which contain carbon having an atomic weight of 14. After tabolism within a period of about an hour, or less, is quite small, it is desirable to contact the solution of the base with extraneous carbon dioxide in order to obtain sufiicient quantity of barium carbonate to assure precipitation and obtention on a filter. The intensity of the radioactivity of the barium carbonate inay then be determined.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

I claim:

1. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from a prospect I zone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of whose molecules contain carbon atoms having an atomic weight of 14 to form a reaction mixture with each of said earth samples, maintaining each of said reaction mixtures at an incubating temperature for a time sufficient for the formation by any microbes contained in said earth samples of microbial metabolism products from the hydrocarbon, and analyzing at least a portion of each of said reaction mixtures for the quantity of carbon atoms having an atomic weight of 14 which have entered into a microbial metabolic process said quantity being a measure of the number of hydrocarbon-consuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit.

2. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from a prospect zone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of whose molecules contain carbon atoms having an atomic weight of 14 to form a reaction mixture with each of said earth samples, maintaining each of said reaction mixtures at an incubating temperature for a time sufficient for the formation by any microbes contained in said earth samples of microbial metabolism products from the hydrocarbon, and analyzing at least a portion of each of said reaction mixtures for the quantity of microbial metabolism products the molecules of which contain carbon atoms having an atomic weight of 14 said quantity being a measure of the number of hydrocarbon-consuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit,

3. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from a prospect zone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of whose molecules contain carbon atoms having an atomic weight of 14 to form a reaction mixture for each of said earth samples, maintaining each of said reaction mixtures at an incubating temperature for a time sufficient for the formation by any microbes contained in said earth samples of microbial metabolism products from the hydrocarbon, and analyzing at least a portion of each of said reaction mixtures for the quantity of material derived from microbial metabolism product the molecules of which contain carbon atoms having an atomic weight of 14 said quan tity being a measure of the number of hydrocarbonconsuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit.

4. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from a prospect zone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of whose molecules contain carbon atoms having an atomic weight of 14 to form a reaction mixture with each of said earth samples, maintaining each of said reaction mixtures at an incubating temperature for a time sufiicient for the formation by any microbes contained in said samples of carbon dioxide from the hydrocarbon, and analyzing at least a portion of each of said reaction mixtures for the quantity of carbon dioxide the molecules of which contain carbon atoms having an atomic weight of 14 said quantity being a measure of the number of hydrocarbonconsuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit. a

5. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from a prospectzone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of whose molecules contain carbon atoms having an atomic weight of 14 to form a reaction mixture, maintaining each of said reaction mixtures at an incubating temperature for a time suliicient for the formation by any microbes contained in said earth samples of carbon dioxide from the hydrocarbon, and analyzing at least a portion of each of said reaction mixturm for the quantity of material derived from carbon dioxide the molecules of which contain carbon atoms having an atomic weight of 14 said quantity being a measure of the number of hydrocarbonconsuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit.

6. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from aprospect zone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of Whose molecules contain carbon atoms having an atomic Weight of 14 to form a reaction mixture with each of said earth samples, maintaining each of said reaction mixtures at an incubating temperature for a time sufiicient for the formation by any microbes contained in said samples of microbial protoplasm from the hydrocarbon, and analyzing at least a portion of each of said reaction mixtures for the quantity of microbial protoplasm the molecules of which contain carbon atoms having an atomic weight of 14 said quantity being a measure of the number of hydrocarbon-consuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit.

7. A geomicrobial method for prospecting for petroleum comprising collecting earth samples from a prospect zone, contacting each of said earth samples with oxygen and with a hydrocarbon at least some of Whose molecules contain carbon atoms having an atomic Weight of 14 to form a reaction mixture, maintaining each of said reaction mixtures at an incubating temperature for a time sufiicient for the formation by any microbes contained in said earth samples of microbial protoplasm from the hydrocarbon, and analyzing at least a portion of each of said reaction mixtures for the quantity of material derived from microbial protoplasm the molecules of which contain carbon atoms having an atomic weight of 14 said quantity being a measure of the number of hydrocarbon-consuming microbes contained in each of said earth samples anomalous variations of which are indicative of the presence of an underlying petroleum deposit.

References Cited in the file of this patent UNITED STATES PATENTS Sept. 1, 1942 May 23, 1944 Sanderson Ta ggart OTHER REFERENCES vol. 8 (1939), pages 

1. A GEOMICROBIAL METHOF FOR PROSPECTING FOR PETROLEUM COMPRISING COLLECTING EARTH SAMPLES FROM A PROSPECT ZONE, CONTRACTING EACH OF SAID EARTH SAMPLES FROM A PROSPECT AND WITH A HYDROCARBON AT LEAST SOME OF WHOSE MOLECULES CONTAIN CARBON ATOMS HAVING AN ATOMIC WEIGHT OF 14 TO FORM A REACTION MIXTURE WITH EACH OF SAID EARTH SAMPLES, MAINTAINING EACH OF SAID REACTION MIXTURES AT AN INCUBATING TEMPERATURE FOR A TIME SUFFICIENT FOR THE FORMATION BY ANY MICROBES CONTAINED IN SAID EARTH SAMPLES OF MICROBIAL METABOLISM PRODUCTS FROM THE HYDROCARBON, AND ANALYZING AT LEAST A PORTION OF EACH OF SAID REACTION MIXTURES FOR THE QUANTITY OF CARBON ATOMS HAVING AN ATOMIC WEIGHT OF 14 WHICH HAVE ENTERED INTO A MICROBIAL METABOLIC PROCESS SAID QUANTITY BEING A MEASURE OF THE NUMBER OF HYDROCARBON-CONSUMING MICROBES CONTAINED IN EACH OF SAID EARTH SAMPLES ANOMALOUS VARIATIONS OF WHICH ARE INDICATIVE OF THE PRESENCE OF AN UNDERLYING PERTOLEUM DEPOSIT. 